Spring framework IoC underlying core principles

5) IoC underlying core principles

5.1) IoC core interface

5.2) Component scanner

• During the development process, necessary beans need to be loaded according to requirements, and specified beans are excluded

5.3) Set component scan loading filter

• Name: @ComponentScan

• Type: Class annotation

• Location: Above the class definition

• Role: set spring configuration loading class scanning rules

• example:

  @ComponentScan(
      value="com.itheima",	           //设置基础扫描路径
      excludeFilters =                          //设置过滤规则，当前为排除过滤
  	@ComponentScan.Filter(            //设置过滤器
  	    type= FilterType.ANNOTATION,  //设置过滤方式为按照注解进行过滤
  	    classes=Repository.class)     //设置具体的过滤项，过滤所有@Repository修饰的bean
      )
  

​ includeFilters: set the inclusion filter

​ excludeFilters: set exclusion filters

​ type: Set the filter type

5.4) Custom component filter

• Name: TypeFilter

• Type: Interface

• Role: custom type filter

• example:

  public class MyTypeFilter implements TypeFilter {
        
        
      public boolean match(MetadataReader mr, MetadataReaderFactory mrf) throws IOException {
        
        
          ClassMetadata cm = metadataReader.getClassMetadata();
          tring className = cm.getClassName();
          if(className.equals("com.itheima.dao.impl.BookDaoImpl")){
        
        
              return false;
          }
          return false;
      }
  }
  

5.5) Custom importer

• The bean can enter the spring container only through configuration, and be loaded and controlled by spring
• The way to configure the bean is as follows:
  • Use tag configuration in XML file
  • Use @Component and derivative annotation configuration
• In the process of enterprise development, usually a large number of beans need to be configured, and a way to configure a large number of beans quickly and efficiently is required

ImportSelector

• Name: ImportSelector

• Type: Interface

• Role: custom bean importer

• example:

  public class MyImportSelector implements ImportSelector {
        
        
      public String[] selectImports(AnnotationMetadata icm) {
        
        
          return new String[]{
        
        "com.itheima.dao.impl.AccountDaoImpl"};
      }
  }
  

  @Configuration
  @ComponentScan("com.itheima")
  @Import(MyImportSelector.class)
  public class SpringConfig {
        
        
  }
  

5.6) Custom registrar

• Name: ImportBeanDefinitionRegistrar

• Type: Interface

• Role: custom bean definition registrar

• example:

  public class MyImportBeanDefinitionRegistrar implements ImportBeanDefinitionRegistrar {
        
        
      public void registerBeanDefinitions(AnnotationMetadata icm, BeanDefinitionRegistry r) {
        
        
          ClassPathBeanDefinitionScanner scanner = new ClassPathBeanDefinitionScanner(r, false);
          TypeFilter tf = new TypeFilter() {
        
        
              public boolean match(MetadataReader mr, MetadataReaderFactory mrf) throws IOException {
        
        
                  return true;
              }
          };
          scanner.addIncludeFilter(tf);
          //scanner.addExcludeFilter(tf);
          scanner.scan("com.itheima");
      }
  }
  

5.7) Analysis of bean initialization process

5.8) Analysis of bean initialization process

• BeanFactoryPostProcessor
  • Role: Defines the actions performed before the bean object is created after the bean factory object is created, and is used to perform post-creation business processing on the factory
  • Run time: The current operation is used to process the factory and only run once
• BeanPostProcessor
  • Function: Defines the unified actions performed before and after the initialization of all beans, which are used to perform pre-creation business processing and post-creation business processing on the bean
  • Runtime: The current operation is accompanied by the creation process of each bean, and the operation is run every time a bean is created
• InitializingBean
  • Role: Defines the actions to be performed before the initialization of each bean, which is a non-uniform action and is used to perform business processing on the bean before creation
  • Runtime: The current operation is accompanied by the creation process of any bean to ensure its personalized business processing
• Note: The above operations need to be loaded by the spring container to run

5.9) Analysis of bean initialization process

5.10) tedious bean initialization process processing

• FactoryBean
  • Encapsulate the initialization process of a single bean to achieve the purpose of simplifying configuration

The difference between FactoryBean and BeanFactory

• FactoryBean: Encapsulate the creation process of a single bean
• BeanFactory: the top-level interface of the Spring container, which defines bean-related acquisition operations